Electrochemical capacitors are a new type of energy storage devices emerged in recent years. They are characterized in having short charging time, long life time, good temperature characteristics, energy conservation and environment friendliness, etc. Comparing with traditional rechargeable batteries (Ni—H batteries and lithium ion batteries), electrochemical capacitors have a larger specific power of an order of above 1 kW/kg and a longer cycle life of over ten thousand cycles. Moreover, electrochemical capacitance is also an energy technology which does not lead to pollution of the environment. With the rise of new green electric vehicles and the development of a variety of electronic communication technologies, people are considering using electrochemical capacitors as a backup power for various storages and using them in combination with batteries to form a hybrid power system for electric vehicles. Accordingly, it is very important to conduct works in theoretical research and practical application of electrochemical capacitors. It is an important direction in future developments of electrochemical capacitors to synthesize electrode materials with nano-structures using nanotechnology, because nanomaterials or nanocomposites can effectively improve the electric capacity and cycle life of the materials due to their special nano-scale structures and morphologies.
In recent years, carbon nanomaterials such as carbon nanotubes, porous carbon, activated graphene, etc., have drawn great attentions as they can acquire a relatively high mass specific capacitance due to their high specific surface areas. However, these carbon materials with high specific surface areas may not be suitable as an electrode material for a supercapacitor, because their densities are usually less than 0.5 g cm−3, resulting in their relatively low area specific capacitance and volumetric specific capacitance, whereas the volumetric specific capacity of a material is important due to the need for designing and manufacturing small-scale energy storage devices. Therefore, it is an important indicator for the electrode material to have a relatively high density.
Graphitized carbon microspheres have drawn broad attentions from researchers as advantages such as dense packing, good cycle performance and low price can be achieved due to their large bulk density. Graphitized carbon microspheres containing fluorine and nitrogen show a good application prospect in many fields, for example, new energy resources and the environmental pollution treatment, etc., due to their special compositions and microstructures. Qiu-Feng Lu, et al. (Journal of Analytical and Applied Pyrolysis, 2012, 93: 147-152) fabricates nitrogen-doped carbon hollow nanospheres by pyrolysis of copolymers, but the resulted material does not exhibit any electrochemical performance. Y. M. Yu, et al. (Fuel cells, 2012, 12:506-510) produces nitrogen-doped carbon hollow microspheres by using silicon dioxide as a template, carbonizing dopamine at different temperatures, and finally de-templating. This preparation method requires high temperature (1000° C.) treatment of the material, and the resulted material does not exhibit a good capacitive performance.